1. Field of the Invention
The present invention relates to an optical device, more specifically, to an array of optical image projection devices where each image projection device projects a portion of an object image onto a surface.
2. Discussion of the Prior Art
A known optical image projection device projects an original image on a sheet of paper or the like through a single lens or a single lens system comprising a plurality of lenses combined into one entity. Such optical systems have only one optical axis and a number of defects are inherent therein.
First of all, the intensity of illumination of the plane of an image decreases according to the distance thereof from the optical axis. Second, the total length of the optical axis of an optical system tends to be too long in order to insure that all the image of an original object matter is properly projected. This is due to the difficulty of providing conventional lenses having a large image viewing angle. Third, the luminance of a projected image is substantially decreased compared with that of the plane of original image matter.
There are also available optical image projection devices devoid of the defects set forth above. These devices employ an array of optical projection devices where each optical image projection device has its own optical axis. Such an array of optical devices may also be known as an aggregated optical projection device.
Referring to FIG. 1, there is shown a prior art array of optical image projection devices where each image projection device comprises a single lens system such as the system comprising lenses 1, 2 and 3. Each image projection device projects a portion of the letter R (see FIG. 1) from sheet D onto sheet P, the portions being hopefully, properly joined or merged on sheet P to form the image of the letter R. Of course, if the portions are not properly merged, they might overlap thereby introducing distortion into the projected image.
The images of an original object matter obtained through the respective lens systems of the above optical image projection device array must be regular, vertical and actual images. One known optical image projection device for effecting this comprises three convex lenses 13, 14 and 15 as shown in FIG. 2 where the system of FIG. 2 may correspond to one of the lens systems of FIG. 1. In the system of FIG. 2, an inverted actual image of a letter R on the surface of a sheet D is projected onto the main plane of convex lens 14 (No. 2) through convex lens 13 (No. 1). The rays of light are then returned in the direction of the optical axis through convex lens 14 and an inverted actual image of the inverted actual image on the main plane of convex lens 14 is produced on the surface of sheet P through convex lens 15 (No. 3) thus obtaining a regular vertical image R' of the original letter R on the surface of sheet P. A regular image can thus be obtained in the orthogonal directions of x and y with respect to the optical axis of the lenses. It is also known to select a curvature of the x direction which is different from that of y, thus obtaining a regular image of the object matter in the x direction and an inverted image thereof in y direction.
The optical image projection device array set forth above is capable of making the total length of the optical axes uniform and equal, irrespective of the size of the object matter and is capable of reducing the total length of the optical axis considerably, compared with the before-mentioned conventional single lens optical system. Further, a high level of illumination intensity can be made available on the image plane. However, in spite of the foregoing advantages conventional optical image projection device arrays are defective in that overlapping or improper merging of sectional images tends to occur.
In order to illustrate in more detail the problems relating to the array of FIG. 1, reference should also be made to FIG. 3. The optical axes 10, 11 and 12 of the lens systems shown in FIG. 1 each have to be a single axis, parallel to one another. Further, the main plane of each lens, for instance, the main planes 16, 17 and 18 of respective lenses shown in FIG. 3, has to be parallel to the planes of sheets D and P. It is especially quite important that each one of the above-mentioned optical axes be a single entity and parallel to the other optical axes. Deviation of an optical axis can result from the susceptiveness of the optical axis of each lens system to deviate from the center of the lens. The deviation of the image on plane P resulting from absence of axis parallelism, is several times the deviation .DELTA.y (see FIG. 3) of the optical axis. As can be seen in FIG. 3, it may be 2.DELTA.y and result in improper image overlapping. The deviation .DELTA.y may be cumulative and comprise the deviation .DELTA.y of the optical axis of lens 22 and that of lens 24.